Effect of 1,25-dihydroxyvitamin D3 on phospholipid metabolism in a clonal osteoblast-like rat osteogenic sarcoma cell line.

T Matsumoto,Y Kawanobe,K Morita,E Ogata

doi:10.1016/s0021-9258(17)38783-5

Abstract

The effect of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) on phospholipid metabolism was examined in clonal rat osteogenic sarcoma cells, UMR 106, of osteoblastic phenotype. Treatment of UMR 106 cells with 10(-8)M 1,25-(OH)2D3 for 48 h caused an increase in [14C]serine incorporation into phosphatidylserine (PS) and a decrease in [3H]ethanolamine, [3H]linositol, and [14C]choline incorporation into phosphatidylethanolamine (PE), phosphatidylinositol, and phosphatidylcholine, respectively; the decrease in [3H]ethanolamine incorporation into PE was the largest. The total contents of phospholipids were similarly affected by 10(-8)M 1,25-(OH)2D3 treatment, suggesting that the effects of 1,25-(OH)2D3 are due largely to alterations in the synthesis of these phospholipids. The effects of 1,25-(OH)2D3 were evident at 10(-10) M 1,25-(OH)2D3, and 10(-8)M 1,25-(OH)2D3 caused a maximal stimulation of [14C]PS synthesis (167% of control) and a maximal reduction in the [3H]PE synthesis (41% of control). The [14C]PS/[3H]PE ratio increased gradually and reached a maximum after 70 h of treatment with 10(-8)M 1,25-(OH)2D3. When the cells were cultured in calcium-free medium containing 0.5 mM EGTA or when 5 microM cycloheximide was added to the medium, the effect of 1,25-(OH)2D3 on phospholipid metabolism was almost completely inhibited. Neither 25-hydroxyvitamin D3 nor 24,25-dihydroxyvitamin D3 caused significant changes in phospholipid metabolism. These results suggest that 1,25-(OH)2D3 alters phospholipid metabolism by enhancing PS synthesis through a calcium-dependent stimulation of the base exchange reaction of serine with other phospholipids and that the effect of 1,25-(OH)2D3 requires the synthesis of new proteins. Because PS is thought to be important for apatite formation and bone mineralization by binding calcium and phosphate to form calcium-PS-phosphate complexes, the present data suggest that 1,25-(OH)2D3 may stimulate bone mineralization by a direct effect on osteoblasts, stimulating PS synthesis.

Highlights

Effects of 1,25-(OH)aD3are due largely to alterations and thathese complexes can nucleate apatite formationfrom in the synthesis of these phospholipids
24,25-dihydroxyvitamin D3 caused significant changes in phospholipid metabolism. These results suggest that 1,25-(OH)zD3altersphospholipid metabolism by enhancing PS synthesis througha calcium-dependent stimulation of the base exchange reactionof serine
While 1,25-(OH)&, the most active metabolite of vitamin D3, is a potent stimulator of bone resorption (12), none of vitamin D3 metabolites including 1,25-(OH)2D3have been shown to possess effects on osteoblasts that can be directly linked to the stimulation of the bone mineralization process

Summary

RESULTS

Incorporation of Labeled Substrates-After treatment of the cells strates into Phospholipids-Preliminary experiments indiwith vitamin D3 metabolites for the indicated period of time, the medium was removed and thecells were washed twice with the same medium without vitamin D3 metabolites They were labeled for 1h in Eagle's medium containing 5%fetal bovine serum with either 0.1 pCi of [3H]ethanolamine and 0.2 pCi of ["Clserine or 0.2 pCi of [3H]inositol and 0.1 pCi of ["C]choline. The chromatograms were developed with ch1oroform:methanol:acetic acidwater (5040T3) Because this syscorporated into PS, PE, PC, and PI, respectively, and that the changes in the incorporation of labeled substrates into lipid fraction by 1,25-(OH)zD3treatment are due mostly to changes in theincorporation into these phospholipid classes.

PI Inositol *

Total lipids

DISCUSSION

None Control